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<b>assume </b><a NAME="E1:50_1_1"/>
 <a href="xboole_0.html#K1">{}</a>  <a href="hidden.html#R2">in</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default"><font color="Maroon">c<sub>1</sub></font></span><a href="tarski.html#K1">}</a></span>
 ; <i><font color="Red">:: according to </font></i><a class="ref" href="setfam_1.html#D9" target="_self">SETFAM_1:def 9</a><br/>

<b>hence </b><a NAME="E2:50_1_1"/>
contradiction
 <b>by </b><i><a class="ref" href="tarski.html#D1">TARSKI:def 1</a></i>;<br/>


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